The land owner should have intimated the Agent before cancelling the GPA. As he has not done so, the Agent can (1) send a legal notice to the owner intimating that based on the GPA, he has entered into a sale agreement with a 3rd party and the sale consideration was paid to the owner vide receipt..... (2) file a civil suit against the land owner for damages.
To safeguard the interest of the Agent, it is better to include a 3rd party as 'sale agreement holder', because through him a criminal complaint also can be lodged.
In these matters, a particular group of marwadi financiers are very sharp. Immediately after getting a scape-goat land owner, they will get GPA registered at IInd Line Beach SRO or Sowcarpet, and within 2 days they will register a mortgage or sale agreement at the SRO where the land is situated. (That's the reason they have captured (!) upto Tirupathi)